When Lasers Took to the Air to Measure the Earth

Submitted by sowmy on Mon, 02/20/2017 - 11:09am

Author:

EVAN ACKERMAN

News Story Date:

2017-02-20 00:00:00

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In 1974, lasers had been around for only 14 years. While there were a few applications in medicine and telecommunications, lasers were not the ubiquitous product that they are today.That year, Allan Carswell, a professor of physics at York University, in Toronto, decided that it was about time for someone to do something useful with a laser, so he and his wife, Helen, founded a company called Optech to commercialize the technology.

In the late 1970s, Optech started selling laser range finders, which use a single beam to determine the distance between the laser emitter and whatever object you pointed it at. Unlike most other range finders then on the market, Optech’s detectors were sensitive enough to work with “noncooperative” targets—that is, you didn’t have to point the laser at a reflector for it to work. By mounting an Optech laser range finder on an airplane and pointing it at the ground, you could then fly back and forth to build a topographical profile, which, when stitched together with other such profiles, formed a low-resolution three-dimensional map.

By the early ’80s, Optech engineers had come up with the idea of scanning the beam back and forth using a mirror, an application that came to be known as scanning lidar (for “light detection and ranging”) [PDF]. The photo, taken for the Toronto Star in 1986, shows Carswell with a model of an aircraft equipped with Optech’s Larsen-500, the company’s first bathymetric lidar system for measuring the depth of water in oceans, lakes, and rivers.

The Larsen-500 was one of the first commercial scanning airborne lidars: Its 15-degree field of view resulted in maps that were easier to make and much more detailed. It also used a green (532-nanometer-wavelength) laser that could penetrate water. In the Arctic, where the water is clear, the Larsen-500 could see 50 meters beneath the ocean’s surface.

In 1985, Optech delivered the Larsen-500 to the Canadian Hydrographic Service (CHS), which is responsible for creating navigation charts of Canada’s coasts and waterways. Until then, the service had made its charts using sonar mounted on a boat, but mapping from an airplane was faster, safer, and more efficient. Three years later, the CHS put out the first ever nautical chart based on lidar bathymetry. (The service still uses sonar, too, but that technology has gotten much more sophisticated.)

Since then, Optech’s lidars have improved substantially, with data rates increasing from 20 hertz to 900,000 Hz in the latest generation. One of the company’s highest-profile projects was for NASA’s Phoenix lander, which touched down on Mars on 25 May 2008, carrying an Optech-designed lidar sensor as part of the Canadian Space Agency’s meteorological station instrument. The lidar shot laser pulses vertically into the air, while a telescopic detector looked for reflections from dust and ice particles, providing data about the Martian atmosphere and Martian weather.